A set of survey data on diapers shows that 20.47% of users will be very concerned about the breathability of diapers when purchasing baby diapers. The sweat glands of the baby's skin have small perspiration holes, which can not control the skin temperature well. If diaper has poor breathability, after the urine is absorbed, the heat and moisture are collected in the diaper which easily make the baby feel stuffy, making the small butt red, swollen and inflamed, causing diaper rash.
When urine is generated, the inside of the diaper become a hot and humid environment. Therefore, from a professional point of view, the so-called breathability actually refers to water vapor permeability, which can be expressed by the water vapor permeability (g / cm2 • 24h). The bottom film that is the outermost layer of the diaper is usually the main factor affecting the breathability of diaper, and it is also the layer that needs to contact baby's skin. The non-woven fabric used in the bottom film uses the difference between water droplets (minimum droplet diameter 20 μm) and water vapor molecules (diameter 0.0004 μm) to achieve waterproof and breathable effects. The following are the performance requirements of each component of the diaper and the choice of nonwovens.
1. Top sheet
The top sheet is the part which directly contact with human skin, so it is required to be dry, comfortable and soft. During the use of diapers, urine needs to pass through the surface layer quickly, so the surface layer needs to have good hydrophilic properties and penetrated multiple times with less back osmosis. Currently, diaper topsheet on the market mainly uses spunbond and hot air nonwoven. Ten years ago, 80% of the diaper topsheet was made of spunbond nonwoven. In recent years, people's pursuit of the softness and comfort of diapers has become more and more intense. Hot air non-woven fabrics are more and more applied to the surface layer because of its fluffy and soft characteristics. Spunbonded nonwoven has high strength, good water absorption, dry and comfortable, it’s still one of the main materials of the topsheet. Through the improvement of the formula and the modification of the equipment, the softness of the spunbond nonwoven fabric is greatly improved, but the fluffy feel is still not as good as hot air nonwoven. Fast penetration, dryness, softness and cotton feel are the development trends of topsheet.
2. Back sheet
The role of back sheet is to prevent urine from leaking out. Early diapers mainly used PE film as the backsheet. As consumers' requirements for comfort increased, non-woven fabric and PE film composite(laminated film) backsheet came into being. The softness of backsheet is one of the important basis for consumers to judge the softness of diapers. Therefore, in addition to the characteristics of imperviousness, less fluff, and good strength, the non-woven fabric for the bottom layer must have a fabric-like soft touch and be wear-resistant. At present, because of low cost, good abrasion resistance, softness, and light weight, spunbond nonwoven is the main material for back sheet. However, due to the soft and fluffy characteristics of hot air nonwoven, many diaper products have been converted to hot air nonwoven in recent years. However, hot air nonwovens are made of short fibers, and the setting effect is not as good as spunbond nonwoven and fluff is slightly more severe. In recent years, many hot air nonwoven manufacturers have greatly reduced fluff by adding ironing rollers and other processes. Soft, cotton-like, abrasion-resistant and thin are the development direction of diaper back sheet.
3. Waist band
Non-woven fabric used for waistband of baby pants needs to be good strength, less fluff, and strong fabric feel. Currently, spunbond non-woven fabrics are mainly used. Some companies have tried to use elastic films and hot air nonwoven to make the waist, but the strength of the hot air nonwoven after bonding seams weak. In addition, although the hot air nonwoven is fluffy, it will be thicker when used for waist, and there is no feel on the hand. What's special is that it is not the main material for waist measurement. Soft, fluffy, wear-resistant and good breathability is the development trend of waistband.
4. Leak guard
The main function of the leak cuffs is to prevent urine from leaking from both sides. Therefore, non-woven fabric for leak guard needs good water repellency, high strength and softness. Currently, mainly used spunmelt nonwoven (SMS). High barrier properties, softness, cotton texture, and thinness are the development trends of leak guard.
5. Core Wrap
The main function of core wrap is to prevent SAP and fluff pulp from loosening and leaking. It is necessary to choose materials with good coverage, hydrophilicity and softness. The previous material mainly was tissue paper. However, due to the poor wet strength of tissue paper, it is easy to break after absorbing water. At present, more and more core wrapping layers use spunmelt nonwovens. Good wet strength, softness, hydrophilicity, and low back permeability are the development trends of core coatings.
The aquisition distribution layer is located under the surface layer, and its role is to accelerate the penetration and diffusion of liquid and reduce the liquid osmosis. The non-woven fabric for the guide layer needs to have the characteristics of hydrophilicity, fast liquid penetration and good liquid diffusibility. In the early days, spunbond nonwovens or perforated films were mainly used as the guide layer, but in recent years, hot-air nonwovens or chemically bonded nonwovens were mainly used, and in order to improve the visual effect, nonwovens of different colors were also used as guides Stratosphere. Increasing the diversion speed, expanding the diversion area, and evenly distributing the liquid are the development trends of the ADL.
7. Frontal Tape
Frontal tape needs to have the characteristics of high strength, easy to stick, no lint, and strong peeling strength. In the past, mainly used spunlace nonwoven fabrics were laminated with films, or spunbond nonwoven fabrics were laminated with films and embossed.Due to High cost, gradually replaced by spunmelt nonwovens. High strength, comfortable feel and beautiful appearance are the development directions of frontal tape.
8. Side Tape
Side tape needs to have the characteristics of high strength, good uniformity, softness and comfort. In the past, mainly use spunlace nonwovens for side tape, but because of the low cost of spunmelt nonwoven, it becomes the mainstream of the market.
The differences between the two widely used diaper surface materials-hot air nonwoven and spunbond nonwoven, and their advantages and disadvantages.
Hot air non-woven
It belongs to a type of hot air bonding (hot rolling, hot air) non-woven. Hot air non-woven fabric is formed by the short fibers after carding, and the hot air on the drying equipment is used to penetrate the web to be heated and be bonded.
After the polymer is extruded and stretched to form continuous filaments, the filaments are laid into a web, and the web is then subjected to self-adhesion, thermal bonding, chemical bonding, or mechanical reinforcement to make the web into a non-woven fabric. Spunbond nonwovens are long fibers but their raw material is plastic chips.
Pros and cons
Hot air non-woven fabric: high fluffy degree, good elasticity, soft feeling, strong warmth, and good air permeability. But its strength is low and it is easy to deform.
Spunbond non-woven fabric: It is made directly from polymer particles after spinning into a web without using fibers, and is heated and pressed by rollers. It has excellent mechanical properties, good tensile strength, elongation at break, and tear strength. , The thickness is very thin, but the softness and air permeability are not as good as hot air nonwoven fabric.
"So generally the surface layer of good diapers is made of hot air non-woven fabric. Spunbond non-woven fabrics are mainly used in medical and sanitary manufacturing, but there are also many diaper manufacturers who choose to use spunbond NW.